There is ongoing development for direct communication between devices in communication system. In recent years, a device-to-device (D2D) communication underlying a cellular network has been studied. The D2D communication allows a direct communication between UEs or devices without passing through a base station. In order to achieve the direct communication between the devices or UEs, a device-to-device (D2D) link is required. By utilizing the D2D link, the UEs or devices belong to the same cell or different cells may directly exchange data each other without passing through a base station or a network.
In order to enable such direct communication between UEs or devices in a current cellular communication system, it is a need to be solved for problems relating to a HARQ processing method between UEs or devices performing transmission and reception through the D2D link. In particular, it is necessary to minimize a HARQ signaling overhead causing by a plurality of UEs or devices in the D2D communication system. Further, in order to control the efficiency of control signaling and to minimize an impact on D2D communication system efficiency, it is necessary to provide an optimized HARQ feedback signaling for a cluster within the D2D communication system